The invention concerns a triple shaft adjusting gear comprising a driving part that can be connected rotationally fast to a drive shaft, a driven part that can be connected rotationally fast to a driven shaft and an adjusting member that can be connected rotationally fast to an adjusting shaft.
Triple shaft adjusting gears are used for instance in internal combustion engines for adjusting phase angles, predominantly for adjusting the opening and closing times of the gas exchange valves (camshaft adjusters, phase adjusters for actuator shafts in variable valve trains). The phase adjuster is arranged as an adjusting member in a triple shaft system. Primarily, the driving power is supplied to the triple shaft system through the drive shaft (e.g. chain sprocket), and this driving power is then delivered through the driven shaft (e.g. camshaft). The adjusting member is arranged within the power flow as a connecting member between the drive shaft and the shaft to be driven. The adjusting member, superimposed by a third shaft (adjusting shaft), enables an additional transfer of mechanical power into the shaft system or a withdrawal of this power out of the system. In this way, it is possible to vary the moving function (phase angle) defined by the drive shaft relative to the driven shaft.
Examples of such triple shaft adjusting gears are wobble plate mechanisms and internal eccentric mechanisms which are described, for instance in WO 2006/018080. This category further includes the shaft mechanisms disclosed in WO 2005/080757 and the mechanisms known from US 2007/0051332 A1 and US2003/0226534 A1.
A variety of phase adjusters are known from the prior art. For example, DE 10 2004 009 128 A1, DE 10 2005 059884 A1 and DE 10 2004 038 681 A1 describe electromechanical camshaft adjusters.
DE 102 48 351 A1 discloses an electromechanical camshaft adjuster in which the adjusting motor is connected to the adjusting gear through a disengageable clutch. Through an adequate design of the clutch, it is possible to limit the torque that can be transmitted to the adjusting shaft. This clutch then acts as a safety clutch.
A special case of a triple shaft adjusting gear is a double shaft arrangement in adjusting drives in which the drive shaft is fixed to the housing, i.e. power is transmitted only between the adjusting shaft and the driven shaft. A device of this type serves to convert a driving power of an adjusting element delivered at a high speed and low load into an output power at a low speed and high load, and is used, for instance in reducing gear devices for adjusting drives in the automotive field as well as in industrial application e.g. robotics.
In order to protect the peripheral components from undesired collisions of components in case of control errors in the actuating system, the adjusting range and the drive power range are limited by a limitation of the rotational angle of one of the three shafts relative to a second shaft or relative to the housing. For this purpose, a mechanical stop made as an integral part of the device is used. In the known prior art of camshaft adjusters, this stop is arranged between the driven shaft and the drive shaft because, as a rule, the adjusting shaft traverses an angle of more than 360°.
In such a configuration, the adjusting shaft, which is not limited directly in the adjusting or drive angle, is decelerated in case of a stop through the transmission kinematics and the rigidity of the transmission components as soon as the power take-off side reaches the limit of the rotational angle. During this event, as a result of the extremely high loads, transmission components can get so strongly deformed that they collide with each other and cause the adjusting member to clamp. Moreover, the transmission components can suffer prematurely from fatigue, or they must be oversized for the normal operation to resist the high loads in case of a non-decelerated stop.